The long term objective of this project has been to characterize and understand those factors and mechanisms in the mother and fetus that contribute to the regulation and increases in uteroplacental (UtBF) and umbilicoplacental (UmBF) during pregnancy, respectively, and how they relate to the general cardiovascular adaptation in pregnancy and development. In the proposed project, efforts will focus on studying the mechanisms that regulate the vascular responses to estrogen, basal UtBF in pregnancy, and attenuated uteroplacental responses to vasoconstrictors. To do this 4 specific aims will be addressed: 1) to further characterize the expression and function of uterine vascular smooth muscle (VSM) nNOS in responses to estrogen and pregnancy; 2) to delineate the role of VSM BK[Ca] and other K+-channels in the maintenance and modulation of UtBF in pregnancy; 3) to characterize and delineate the mechanisms that regulate UtBF during parturition; and 4) to determine the role lipid mediators derived from arachidonic acid via the cytochrome P450 (CYP) enzymes play in estrogen responses and the modulation of UtBF in pregnancy. To achieve these aims, we will study chronically instrumented nonpregnant and pregnant ewes with their fetus. In in vivo studies, we will "isolate" the uterus by instrumentation and study uterine vascular responses to multiple agonists and antagonists independent of systemic effects. This permits us to answer specific questions about uterine responses to exogenous E2beta, the role of nitric oxide isoforms, activation of K+-channels, involvement of P450 enzymes, and if endogenous placental estrogen regulates each of these during parturition. In vitro studies are designed to compliment studies in intact animals, permit exploration of signaling pathways, and to characterize estrogen receptor and channel activation and expression in pregnancy. The result of the proposed studies will provide important new understanding of mechanisms regulating blood flow, which are essential to the successful outcome of pregnancy, normal fetal growth, and the maintenance of fetal well-being. This will contribute to our understanding of abnormal fetal growth and how to prevent adverse fetal outcomes.